Popular White Paper On This Topic

Only in a case that you do regular "shutdown" meaning without the "-F" flag you have 1 minute to do a "ps" command find the shutdown process and kill it before the 60 seconds expire. Otherwise it starts killing processes and as Randy said you better let that machine reboot or you have a zombie on you hand and we all know zombies are not fun because all you can do with them is shoot them in the head

You brought up a good Interesting point about "halt -q"
In the old days we used to use "halt -q" to test HA cluster failover that was our way to show customer that no matter what we will failover. Come to find out that many times a few databases would be corrupted even when the JFS was ok, the content was more than likely messed up and Oracle was not very big for us back then. HMC was not very popular either. But now a days even with Oracle I just use the HMC operations to issue fast restart on the AIX LPAR rather than halt -q. This is a lot cleaner and it accomplished the same thing. I really cannot think of any instance when I would need to do "halt -q" anymore.

Once the shutdown starts you are better off letting it finish. It is shutting down services. If you were able to stop it, which I doubt, you would find very quickly that things aren't working as you expect them to.

If your shutdown is in a wrapper script, then you can stop your shutdown if you are VERY VERY quick.
Did you know that you can speed up your shutdown command with ctrl-c ? Do it just when you are in a hurry and when you are waiting for certain things to stop, like when you are waiting for the cas and the platform agents are taking their time to shutdown. Also with unmounting of some file systems - this can be dangerous, so plan your shutdowns accordingly.

For the kill command - run "man kill" and go look at all the signals.
My rule of thumb is to "kill <procnum>" and if that doesn't work, then I "kill -9 <procnum>". The -9 is more harsh, because of the way the signal works.

If you want to throw all your dolls out of the pram, then you can "kill -9 -1" - this will stop your user ID and all connected processes dead in its tracks.

If you have undead living in your OS (zombies that doesn't go away), my rule of thumbs is to start high and work your way down:
kill -15 <procnum>
kill -13 <procnum>
kill -11 <procnum>
kill -9 <procnum>

If this Zombies stays still, then you will have to reboot to get it away.

If you cannot break out of something, then it is meant to be. You do not necessarily want to have a half-shutdown system.

If you want to rip the dam from underneath the duck - "halt -q" BUT I NEVER TOLD YOU THIS. It stops the box DEAD without doing a thing, except starve the system from electricity (PowerVM).
The fastest to the slowest way:
1. reboot -q and halt -q
2. halt and reboot
3. shutdown -Fr -DO-IT-THIS-SAFE-WAY-
4. reboot
5. shutdown
6. reboot